Analysis of concentration dependence of optical conductivity of BaPb1-xBixO3 revisited

The frequency and concentration dependence of the reflectivity in the syste m BaPb1-xBixO3 is fitted with a "double-damping-Drude" model in a wide ener gy range, from the very far-infrared to the visible (2 meV-3 eV). This proc edure is shown to yield better confidence in the deduced spectral conductiv ity than a Kramers-Kronig transformation. The analysis of the spectral cond uctivity is seriously reconsidered, in particular, the high-frequency refle ctivity edge is reassigned to a complex zero of the dielectric response whi ch is the net effect of two different contributions, a charge-carrier "doub le-damping-Drude" and a localised oscillator which is mainly the signature of the CDW gap when the Bi concentration exceeds 0.33. (C) 1999 Elsevier Sc ience Ltd. All rights reserved.